1. Field of the Invention
The present invention relates to a phase shift mask and a manufacturing method thereof, and more particularly, to a half-tone phase shift mask and a manufacturing method thereof which enables only a predetermined portion of exposed light to pass therethrough.
2. Description of Prior Art
Semiconductor devices have had a tendency to be light, thin, short, and small, and consequently, the sizes of unit elements thereof such as transistors and capacitors have also come to be small, so that the patterns thereof are accelerated to be fine and precise.
Generally, in a light emitting mask which is used in a light emitting process to form a pattern, a non-transmissionable film such as chrome is deposited on a quartz substrate, and then a non-transmissionable pattern is formed by ion beam etching. However, it is difficult to form a fine pattern lower than the light resolution ability by the above light emitting mask, and it is impossible to achieve a fine pattern lower than 0.5 .mu.m by conventional photoresist films and with light emitting equipment currently in common use.
Further, ultra high-integrated elements above 64 DRAM require a finer pattern lower than 0.4 .mu.m, the formation of which is realized by a phase shift mask which enables the formation of a photoresist film of high resolution.
FIG. 1 is a sectional view of a conventional half-tone phase shift mask 10, which is widely and commonly used because the manufacturing process of the mask is relatively simple and the resolution of the mask is high, and because the manufacturing redundancy thereof is high. In manufacturing a half-tone phase shift mask 10, a thin chrome film 13 and a phase shift film 15 are first laminated on a transparent substrate 11 such as quartz substrate, and a photoresist film pattern, which is not shown, is formed thereon. A pattern is then formed by etching the predetermined light-exposed portions of the chrome film 13 and the phase shift film 15. Lastly, the photoresist film is again removed.
In this case, it is significant that the thin chrome film 13 must be formed in such a manner that only 5 to 15% of the incident light can transmit therethrough, and it is very difficult to achieve the required light transmission degree thereof. When the degree is 10% higher than the predetermined degree, an undesired pattern is formed.
FIG. 2 is a diagram showing the distribution of light passed through the above half-tone phase shift mask when the transmission degree is 10% higher than a predetermined degree, in which a portion 1 in which the intensity of the light is high is an area exposed to the light, another portion 5 in which the intensity of the light is low is another area unexposed to the light, and another portion 3 in which the intensity of light is zero is a boundary area between the areas exposed and unexposed to the light.
When the photoresist film 17 applied on the substrate 12 is exposed to the light in accordance with the light distribution shown in FIG. 2 and then is developed, the photoresist film pattern is formed as shown in FIG. 3. That is, the photoresist film applied on an area unexposed to the light is exposed to a light having a low energy, and the photoresist film in the area exposed to the light is thereby removed in the developing process.
As described above, as the photoresist film of the area unexposed to the light is removed by a certain thickness, a serious problem can be encountered in progressing the manufacturing process of the ultra high integrated semiconductor device.
Also, in manufacturing the conventional half-tone phase shift mask, the vapor deposition of the chrome is carried out in order to adjust the light transmission degree of the chrome film, and then the chrome is etched by a certain thickness. However, it is very difficult to obtain the desired light transmission degree with this method.